A problem constantly present in several branches of industry is the removal of floating contaminants of various liquids originating from various technologies. The rapid increase of the contamination of environment has called attention especially to the purification of industrial sewages and--taking into consideration also the economic aspects--to their recovery.
The floating contaminations in industrial sewages and other by-products in a liquid state can be divided into two groups according to the liquid to be purified, namely to substances of higher specific weight and to those of lower specific weight than that of the liquid in question. A further division is possible according to the solid or liquid state of the floating substance.
Numerous processes and equipment for the separation of substances of different state, specific weight and grain size are known. The individual or combined carrying out of precipitation, centrifuging and filtering processes is generally a power-consuming task, therefore where the by-pass of larger quantities of substances is necessary, precipitators requiring specifically the lowest energy, having the highest permeability and requiring the lowest establishment costs and operating costs are generally used alone or combined with other technological devices as required.
A detrimental property of the known precipitators-especially if the liquid to be purified contains impurities of both higher and lower specific weight, such as in the case of industrial sewages containing simultaneously sand and oil contaminations--consists in that requirements mutually depreciating to each other are combined in the same system.
In the various sedimentation basins of the most widely used systems and separating basins the sewage is coursed in laminar flow at a minimum speed in order to let settle the floating sand grains on the bottom of the basin, and to let ascend the oil drops to the surface. Since the ascended oil film is generally separated from the surface of the sewage by means of a separating or stripping device suspended into the basin, the sewage should be coursed at least at a speed rendering efficient the separation. Obviously, these two requirements are simultaneously impractical, therefore only a compromise is possible.
Another condition depreciating the practicality of meeting both of the above demands consists in that the sewage load is by no means uniform and its variation is sporadic. These sporadic variations, however, disturb the laminar flow and cause wave phenomena, especially on the surface, but also on the bottom agitating thus the already settled grains, and causing the liquid level to continuously vary in the basin, so that the separating element is sometimes freely hanging in the air and sometimes completely immersed in the liquid, carrying out no separation, or the wave sweeping in and the separating element being just on the surface fills the discharge channel with water and deteriorates the efficiency of separation or even prevents it.
To solve the above problems, a solution is presented in the Hungarian patent specification No. 169.472 according to which the stripping device is arranged on floats and is equipped with at least one row of nozzles, while the edge of the stripping blade is adjusted to or beneath the boundary surface of the sewage to be purified and the contamination ascended to the surface thereof.
The sole detrimental property of the known solution is with respect to the "quality" of the separated contamination, since it contains always a small quantity of the liquid to be purified. The edge of the stripping blade cannot be adjusted exactly to the boundary surface, so that the stripping blade is dipped in the liquid to be purified and the oil carries with it some water into the collecting channel.